As a recording method utilizing the phase change, a method has been known wherein the crystal structure of a metal or a semiconductor is reversibly changed by affecting energy beams or an energy flow such as light or electric current (Joule heat) (Appl. Phys. lett., Vol. 18 (1971), pp. 254–257, U.S. Pat. No. 3,530,441).
Used practically at present as a means for recording on an information recording medium employing a phase-change type recording material, is a means to utilize a reversible change between the crystalline phase and the amorphous phase. Specifically, it is a means to let the crystalline state in a non-recorded/erased state and to form amorphous marks at the time of recording. Usually, a recording layer is locally heated to a temperature higher than the melting point and then rapidly cooled to form amorphous marks. On the other hand, the recording layer is heated at a temperature of approximately at most the melting point and at least the crystallization temperature, and slowly cooled so that the recording layer is kept at a temperature of at most the crystallization temperature for a certain retention time to carry out recrystallization. Namely, in general, a reversible change between the stable crystalline phase and the amorphous phase is utilized, and the information is recorded or retrieved by detecting the difference in physical parameters such as refractive index, electric resistance, volume and change in density, between the crystalline state and the amorphous state.
On the optical information recording medium among information recording mediums, recording and retrieving is carried out by utilizing a change in the reflectivity accompanying the reversible change between the crystalline state and the amorphous state caused locally by irradiation with a focused light beam. Such an optical information recording medium having a phase-change type recording layer is being developed and used practically as a low cost large capacity recording medium excellent in portability, weather resistance, impact resistance, etc. For example, a rewritable phase-change type optical information recording medium (hereinafter a phase-change type optical information recording medium may sometimes be referred to simply as “phase-change type optical disk”, “optical disk” or “disk”) such as CD-RW, DVD-RW, DVD+RW and DVD-RAM is widely used. Further, it has been developed to achieve a high density by the use of blue laser or by an increase in NA of an objective lens, or to make high speed recording possible by improvement of the recording pulse waveform.
As a material for such a phase-change type recording layer, a chalcogenide alloy is used in many cases. As such a chalcogenide alloy, a Ge—Sb—Te type, In—Sb—Te type, Ge—Sn—Te type or Ag—In—Sb—Te type alloy may, for example, be mentioned. Such an alloy is usually an overwritable material also.
Here, overwriting is a means wherein when recording is carried out again on a once-recorded medium, writing is carried out without erasing before the recording, that is, a means of recording while erasing. On a phase-change type optical information recording medium, recording is carried out usually by overwriting, and accordingly recording while erasing (i.e. overwriting) may sometimes be referred to simply as recording.
In recent years, along with increase in the amount of information, it has been desired to develop an information recording medium (particularly optical information recording medium) on which recording, erasing and retrieving at a higher speed are possible. As a material capable of satisfying both characteristics of excellent jitter characteristics and storage stability of amorphous marks even in such very high speed recording, a material containing as the main component a ternary composition of Sb—Ge—In is mentioned (JP-A-2001-39031, JP-A-2002-347341). This material is promising as a material to be used for a phase-change type optical disk on which high speed recording and erasing of information signals are carried out at a reference clock period of at most 15 ns.